Micro-patterning of surfaces has been exploited for some time in various applications, such as lithography for semiconductor device fabrication. More recently, various nano-patterning techniques have been developed in order to controllably pattern a surface at smaller length scales than provided by conventional micro-patterning techniques. Some known nano-patterning approaches are based on scanning probe microscopy.
For example, U.S. Pat. No. 6,635,311 and U.S. 2004/0008330 relate to a nanolithography process where a probe tip is connected to a surface to be patterned by a water meniscus which can naturally form between the tip and surface. Material transport from the probe to the surface through the water meniscus provides nano-scale patterning. This approach often requires significant environmental control (e.g., temperature, humidity and gas composition control as considered in U.S. Pat. No. 6,737,646) in order to ensure operation as desired. This approach can be regarded as a direct nano-patterning method, since the surface being patterned is modified directly by the tip.
Alternatively, indirect nano-patterning via scanning microscopy entails use of a scanning microscope to pattern a resist, which is then further processed to pattern an underlying surface. Examples of indirect patterning are considered in U.S. 2004/0131843 and U.S. 2004/0127025. Direct nano-patterning methods are often preferable to indirect methods, since significant difficulties in transferring a nano-scale pattern from a resist to the underlying surface can arise.
Another example of direct nano-patterning is considered in an article by Utsugi (Nature, v347, pp 747–749, October 1990). In this work, a surface of a sample of AgxSe is directly patterned by a scanning tunneling microscope (STM) probe tip. The probe tip in this work does not make physical contact with the surface. A tunneling current of electrons flows between the tip and the sample, on the order of 0.1 nA. The features formed in this work are permanent trenches. The mechanism for feature formation is believed to be field-induced segregation of Se− ions at the surface, followed by reduction of the Se ions to H2Se in a H2 or H2O containing atmosphere. Since H2Se is a gas, a permanent trench is formed. For some applications (e.g., erasable memories) it is preferred that the nano-patterned features be erasable. The approach of Utsugi is inappropriate for such applications.
Information storage is a significant application of micro-patterned or nano-patterned surfaces. The use of a microscope probe tip to provide data storage by inducing localized electrochemical reactions is considered in U.S. Pat. No. 5,434,842. More specifically, patterning of materials having a reversibly modifiable charge state (or which dissociate into components) upon withdrawal or injection of electrons is considered. However, the materials considered in this work (e.g., a mixed monolayer of ferrocene-terminated and unsubstituted alkanethiols coadsorbed on a gold surface, or other self-assembled monolayers) can be difficult to work with and/or environmentally sensitive.
Accordingly, it would be an advance in the art to provide direct, erasable, environmentally insensitive nano-patterning of a surface.